1. Field
The present invention relates generally to communication, and more specifically to techniques for supporting roaming among CDMA communication networks.
2. Background
Wireless communication systems are widely deployed to provide various communication services such as voice, packet data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources. Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, and frequency division multiple access (FDMA) systems. A CDMA system may implement one or more CDMA standards such as IS-2000, IS-95, W-CDMA, and so on. A TDMA system may implement one or more TDMA standards such as Global System for Mobile Communications (GSM). These standards are well known in the art.
A network operator (i.e., a service provider or a “carrier”) may deploy one or more wireless communication systems to provide services for its subscribers. Each deployed system covers a particular geographic region (e.g., a city) and may in turn include one or more smaller networks. For IS-95 and IS-2000, each system is identified by a system identification (SID) value, and each smaller network within a given system is identified by a network identification (NID) value.
For IS-95 and IS-2000, each mobile station maintains a preferred roaming list (PRL) that contains information to assist the mobile station perform system selection and acquisition. The preferred roaming list identifies “permitted” systems/networks that the mobile station can access and (optionally) “forbidden” systems/networks that the mobile station cannot access. These permitted and forbidden systems/networks are identified by their assigned (SID, NID) pairs in the preferred roaming list.
IS-95 and IS-2000 systems are widely deployed throughout the world. Operators of these systems in different countries may collaborate together in order to provide international roaming for their subscribers. However, international roaming is complicated by the manner in which the SID and NID and the preferred roaming list are currently maintained and used. In particular, there are several issues with respect to the preferred roaming list for international roaming. First, maintenance of the preferred roaming list for multiple network operators is cumbersome. Each network operator would need to collect network configuration information from its roaming partners in order to construct the preferred roaming lists for its own subscribers. The network configurations of each network operator continually evolve. If a network operator changes its network configurations (e.g., add or change a SID or a NID), then all of the roaming partners may need to update their preferred roaming lists accordingly based on the new configurations. PRL maintenance is thus complex and may discourage network operators from supporting international roaming. Second, the size of the preferred roaming list may be large for a large composite network formed with the systems of the roaming partners. The current design of the PRL allows a single (SID, NID) pair to be stored per entry. This PRL design requires a large number (e.g., hundreds) of entries to be present in the preferred roaming list for a large composite network with many (SID, NID) pairs. A large preferred roaming list may significantly impact memory requirements for a mobile station. Moreover, since the preferred roaming list may be sent to a mobile station via over-the-air signaling, a large preferred roaming list would also adversely impact download time.
There is therefore a need in the art for techniques for supporting international roaming and which address the PRL issues described above.